Non-destructive inspection (NDI) of structures involves thoroughly examining a structure without harming the structure or requiring its significant disassembly. Non-destructive inspection is typically preferred to avoid the schedule, labor and costs associated with the removal of a part for inspection, as well as avoidance of the potential for damage to the structure during such disassembly and subsequent reassembly. Non-destructive inspection is advantageous for many applications in which a thorough inspection of the exterior and/or interior of a structure is required. For example, non-destructive inspection is commonly used in the aircraft industry to inspect aircraft structures for any type of internal or external structural inconsistencies in the structure. Inspection may be performed during manufacturing or after the completed structure has been put into service, including field testing, to validate the integrity and fitness of the structure.
Various types of sensors may be utilized to perform non-destructive inspection. One or more sensors may move over the structure to be examined and receive data regarding the structure from which internal structural inconsistencies can be identified. For example, a pulse-echo, through-transmission or shear wave sensor may be utilized to obtain ultrasound data that may be utilized for thickness gauging, detection of laminar defects and porosity and/or crack detection in the structure. Resonance, pulse echo or mechanical impedance sensors may also be utilized to provide indications of voids or porosity, such as in adhesive bond lines of the structure. The data acquired by the sensors is typically processed by a computing device, and the processed data may be stored and/or presented to a user via a display.
Certain types and configurations of structures provide particular challenges during efforts to non-destructively inspect the structure. For example, some structures include a curved surface which may render efforts to non-destructively inspect the curved portion of the workpiece more difficult or at least render the results less detailed than desired. The difficulties presented by non-destructive inspection of structures having curved surfaces is particularly apparent in instances in which the curved surface is a compound curve having different portions with different respective radii of curvature. While a variety of structures having curved surfaces may present challenges for non-destructive inspection, one particular example is a composite structure that defines a shear tie, such as utilized during the manufacture of aircraft. In this regard, a shear tie defines an arc spanning about 90° and includes two or more portions that each have a different respective radius of curvature.
In order to inspect a workpiece having a curved surface, such as a shear tie, inspection probes are utilized that include a plurality of transducers positioned in an arcuate fashion in order to introduce ultrasonic signals into the structure and to receive ultrasonic signals returning from the workpiece. As a result of the size of such traditional transducers, conventional ultrasonic probes are disadvantageously required to space the transducers in fairly wide angular increments, thereby leading to non-destructive inspection results that have a relatively low resolution. By way of example, in order to inspect a shear tie that spans 90° and has an arc length of 0.59 inches with an inspection probe that includes five traditional transducers that are each about 0.25 inches in diameter, the transducers which would have to be divided into two or more rows since the cumulative size of the five transducers is more than twice the arc length of the shear tie. Even in this instance in which the inspection probe would include five transducers placed in two or more rows, the transducers would still be placed at angular increments of 18° so as to extend relatively evenly about the shear tie. As such, the resolution of any one transducer of the inspection probe of this example would also be 18°, which may not be sufficient for some applications. In order to improve the resolution of the inspection probe, the inspection probe can include additional transducers which, in turn, creates additional rows of transducers and, in turn, a larger inspection probe, thereby disadvantageously making the inspection probe more difficult to maneuver.
A conventional inspection probe utilized to non-destructively inspect a structure having a curved surface also generally transfers less energy than desired into the structure as a result of the use of traditional transducers that are individually fired or actuated. In an effort to increase the energy transferred into the structure and, thereby, increase the depth and quality of the inspection, the transducers can be actuated with larger driving voltages, and the receiver that receives the signals returning from the structure may be configured to have a higher gain. However, the use of higher driving voltages and higher gains disadvantageously require the inspection probe to consume more energy.
Additionally, ultrasonic inspection probes generally require a couplant, such as water, between the transducers and the structure to be inspected in order to efficiently couple the ultrasonic signals between the transducers and the structure. Typically, water is provided between the inspection probe and the structure such that a pool of water is on the face of each transducer. Since the efficient transmission and reception of the ultrasonic signals are dependant upon the presence of water on the face of each transducer, the inspection speed, that is, the speed at which the inspection probe is capable of being moved along the structure while continuing to effectively interrogate the structure, is limited by the ability to maintain the water in ample supply on the face of the transducers. As the number of transducers increase, such as to five or more, and the speed at which the inspection probe is moved increased, the amount of water required to effectively couple ultrasonic signals into and out of the structure disadvantageously increases. Particularly for hand-held or portable inspection probes, the necessity to provide a sufficient quantity of water may prove quite cumbersome and difficult to manage.
Accordingly, it would be desirable to develop an improved method and apparatus for inspecting workpieces having a curved surface including, for example, a workpiece having a curved surface with portions having different respective radii. In this regard, it would be desirable to provide an improved method and apparatus for inspecting a structure having a curved surface that could provide inspection results with improved resolution, while avoiding excessive energy consumption and couplant usage.